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Fire plays a critical role in breaking hard-seeded dormancy and establishing seedlings of several Acacia species in and and semi-arid regions. Numerous studies have reported an increase in seedling densities of some Acacias after fire without identifying the exact cause. However, it is generally believed and speculated that the effect is largely physical and heat related. Recent studies have revealed that smoke generated from wildfires has the ability to stimulate seed germination and also to improve seedling vigour. This stimulatory characteristic of smoke has now been confirmed by the isolation of a butenolide (3-methyl-2H-furo[2,3-c]pyran-2-one) from plant smoke that actively promotes germination of many plant species.

The species of Acacia investigated were A. hebeclada (deciduous shrub), A. mearnsii (invasive tree, native to Australia) and A. robusta (deciduous tree). Seeds of A. hebeclada germinated under different light conditions with smoke-derived butenolide solution (10(-7) M), exhibited a significantly (p < 0.05) greater germination percentage than untreated seeds. Whereas A. mearnsii seeds exposed to constant dark conditions showed a significantly (p < 0.05) better germination percentage than the control. However, there was a non-significant improvement for A. robusta seeds. All three species responded positively to the butenolide treatment (10(-7) M) after incubating for 10 days under constant dark conditions at 25 +/- 0.5 degrees C, achieving a higher vigour index and seedling mass in comparison to the controls. Smoke-water (1:500) had an intermediate effect on these species. This study shows that the butenolide, isolated from smoke, may have a significant effect on the post-fire seedling ecology of Acacias. (c) 2006 Elsevier Ltd. All rights reserved.